LMP-103S is the name of a new monopropellant, tested on the PRISMA mission in 2010. It's main ingredient is ADN (Ammonium Dinitramide), a strange chemical invented in the 70's in USSR and independently invented in the West in the early 90's.

The Swedish Company that owns the intellectual rights to this fuel and operated it on PRISMA have reported 6% better specific impulse and 30% better density impulse than Hydrazine. LMP-103S is also a much safer liquid: stable, not sensitive to shock, air, or moisture, not very toxic or corrosive, and has good temperature ranges for storability and use. It also uses a catalyst to "ignite" and "burn" the liquid.

The chemical makeup is reported as 60-65% ADN, 15-20% methanol, 3-6% Ammonia, and the remainder is water. These percentages are by mass, not volume. The exact percentages are still a trade secret.

So now the questions begin:

What's taking so long? Why hasn't it replaced nasty Hydrazine? It's been 5 years now, with not much more heard. Is LMP-103S too good to be true?

Why use methanol instead of ethanol? Ethanol has about 33% more energy per kg and is otherwise very similar in properties such as miscibility.

What is the temperature in the combustion chamber? For the record, for Hydrazine its usually around 800 C, so as long as LMP-103S is not greater than this, it can't be a disadvantage. Nevertheless, in all my searching, I have never been able to find what the temperature of "combustion" is in the combustion chamber.

Does it leave behind any solid residue from the burn? Such as salts? This could be a major disadvantage. Or does it corrode metals or other materials?

Also, in all my searching, I did find one disadvantage but don't know what it means. LMP-103S is not "cold-startable", but Hydrazine is. What does that mean?

$\begingroup$The ethanol vs. methanol question assumes combustion (reaction) with oxygen, right? I don't know what all reactions LMP-103S goes through when it's run across its catalyst, but the methanol may well not be playing a role of "burning" in the usual sense, so its different chemical makeup may actually be an advantage. Alternatively, ethanol might be a liability for some reason in that environment.$\endgroup$
– CBHackingNov 2 '17 at 1:06

4 Answers
4

LMP-103S and hydrazine differ in more ways than that hydrazine unlike LMP-103S is highly toxic and carcinogenic and that LMP-103S has higher performance.

LMP-103S requires more catalyst heating to burn and the burning temperature (about 1600 C) is considerably higher than for hydrazine (about 800 C).

The propulsion system and thus also the on-board software must take into account and ensure that the thruster-catalyst used is really hot (about 350 C), i.e. if the preheating due to a technical failure has failed and thrusting has been started, the whole mission could be lost.

A hydrazine thruster start burning without preheating of the catalyst, i.e. there is no absolute need to be properly functioning and the power required for normal heating is significantly less than that of LMP-103S.

In addition, hydrazine and LMP-103S have different properties as liquids and all valves that previously was qualified for hydrazine must first be space-qualified for LMP-103S to be safely used in space, i.e. in weightlessness & vacuum.

Finally, all planned firings with the HPGP propulsion system on Prisma have been successfully been completed.
On Friday night, September 9th, a 75 sec continuous firing was performed; the longest yet with a HPGP thruster in space, and the accumulated number of pulses exceeded 50,000.
363 sequences have been fired and 63% of the propellant has been consumed.
2 kg of the HPGP propellant remains which will be used for providing ΔV for new mission objectives during the remainder of the mission before decommissioning.
After 15 months in space, with no indications of degradation the flight demonstration is evolving into a space flight qualification.

From EU Horizon 2020 Project Rheform - A most important document
Dated 15.th of June 2015

More than 344 sequences comprising over 50,525 pulses have been performed in continuous, pulse or off-modulation mode.
Performance mapping has been performed by executing firing sequences with pulse durations from 50 ms up to 100 s and pulse mode firings have been performed with duty cycles ranging from 0.1 % to 99 %.
Pulse trains lasting up to 90 min have been executed.
Pulse mode and single impulse bit predictability has been demonstrated to be very accurate for the HPGP
system.
The accumulated burn time is more than 3.5 h to date and 76 % of the propellant being consumed.
Theremaining propellant will be used to provide ?V for extended mission objectives before eventual decommissioning.

During the rendezvous phase in August 2014, there was a problem with one of the propulsion system on PRISMA and the PRISMA project could not catch the opportunity to execute the inspection before the fly-by of Picard.

SNSB (Swedish National Space Board) January 27:th 2015

We're just discussing how to best use the fuel remaining in the HPGP system and if de-orbit can be combined with something else.

SNSB February 23:th 2015

It is, as said hydrazine which is at the end, not the LMP-103S. The HPGP system works just fine and will be used for the maneuvers remaining. Both systems have been used in parallel until the hydrazine ended.

The ECAPS LMP-103S based HPGP systems has performed extremely well on-orbit for five years in support of the PRISMA satellite.

SNSB September 8:th 2015

Mango has in 2015 been given the task to circularize / lowering its orbit to reduce the risk of collision. In connection with this, the HPGP system is used and has thus been able to demonstrate 5 years of operational capability in space.

$\begingroup$Hi and welcome to space.SE! You used to work for Swedish Space Corporation? You're exactly who I want to talk to!!! First off, is there a public source for the burning temp of 1600 C? It doesn't appear to be in the two patent links you provided.$\endgroup$
– DrZ214Jun 27 '15 at 20:41

$\begingroup$Thanks I found that pdf. I want to ask a more complex question now. Why was methanol used instead of ethanol? Ethanol has a lot more energy per kg, and it less toxic than methanol, and I don't see why it would not be compatible in the ADN-Ammonia-Water solution.$\endgroup$
– DrZ214Jun 28 '15 at 15:01

$\begingroup$I would just like to thank you one more time for all the info you've provided. You are a valuable inside source for this sort of thing. I recently posted a related question, space.stackexchange.com/questions/10032/… , and would like to invite you to help out if you can.$\endgroup$
– DrZ214Jul 19 '15 at 3:07

I'm the SkySat propulsion lead and have been flying LMP-103S since June 2016 when SkySat-3 launched from India.

To answer the question:

Yes it is viable and has a number of advantages, mostly the (Isp * density) is much better than hydrazine. But, right now the engines are more expensive to build than those running hydrazine (due to higher combustion temperature, cost of propellant not really an issue).

Really it comes down to what your mission values (cost, complexity of CONOPS, lots of flight heritage, or minimizing size), but it is a serious contender for missions which previously would be hydrazine.

$\begingroup$This is the sort of thing that rather needs a reference. Do you have any thoughts about where one might be found?$\endgroup$
– kim holderNov 12 '15 at 2:24

3

$\begingroup$Citation would be good, but I hafta be honest: I dont have much trouble believing that it currently costs around 5000/kg. That's almost certainly because it's being made in special research plants not set up for mass production. LMP-103S is basically ADN mixed with common liquids (ammonium, water, methanol). IDK how hard it is to make ADN (N4O4H4) but it's gotta be mass produceable somehow. Price comes down when demand incentivizes the increase in supply, but then demand doesn't go up all on its own especially when its expensive. +1 for comparing it to cost of hydrazine.$\endgroup$
– DrZ214Nov 12 '15 at 4:40